Lead pigments and methods of making same



Patented May 29, 1945 LEAD "Gm! AND IITHODS OF I sssxmo 8m Louis E. Barton, Windsor, Conn.

No Drawing.

12 Claims.

In my copending application for patent Serial No. 428,035, filed January 24, 1942, I have disclosed a process of stabilizing lead silicate pigments against discoloration by light, and accelerating the reaction during formation of the pigment. The process consists in combining lead oxide and silica in the solid phase in the presence of a halogen to form an essentially pure lead silicate with a small amount of a chemically combined halogen. In the process referred to the halogen is limited to not more than 5%, for,

though larger quantities are effective in stabilizing the product and accelerating the reaction they unnecessarily change the chemical composition of the pigment, reducing the percentage of lead silicate, the characteristic properties of which it is desired to retain.

I have now found that useful light-stable lead pigments can be made which contain larger amounts of the halogen elements with lead silicate than is permissible in the product or my earlier process referred to. The process of preparing my new lead pigments consists in making a mixture of such lead, silicon and halogen compounds as will, upon heating, supply to the product respectively only lead oxide, silica and the halogen, the halogen being more than 5% 0f the combined weights of lead oxideand silica, and the halogen compound used consisting of halogen combined with a component which is volatiliaed at the temperature of reaction and then heating the mixture until the ingredients chemically combine in the solid phase to form a white pigment.

The chemical reactions and combinations in the formation of my P sments are not definitely known and doubtless vary with diil'erent proportions of ingredients. but for purpose of description I shall refer to the products as lead silicohalides and express chemical compositions as proportions of normal lead halide and lead silicate. That the chemical constitution of my pigments is, in reality, more complex is indicated by some of their observed properties. For example, the normal lead halides areknown to be appreciably soluble in water, but the lead silicohalides made by my process are insoluble in water, indicating the formation of some basic lead halide or other combination.

Icanmskebymyprocesaleadsilicoehalides contsininganydesiredproportion ofleadhalide andthebalanceleadsilicateaswillbehereinafter shown. by examples. 0! the halides, I have found the group comprising chlorine, fluorine and bromine particularly applicable in preparing Application February 8, 1m. Serial No. 474,.

my pi ments since the normal halides, and apparently the basic halides, are white. Iodine 110 Wed in mp rtions much more than 5% since normal lead iodidehas a bright yellow color which prevents the preparation of a white product if larger quantities are used.

An important feature of my process from an industrial and economic standpoint is that the larger amounts of halogen compounds used so accelerate the formation of the pis ent in the solidphase thattheoperationcanbennishedin a short time at comparatively low temperatures. The physical properties of my lead silico-halide pigments vary with composition and the inherent properties of the particular halide used but they retain in a considerable degree the durability characteristic of lead silicates when the pigments are mixed with suitable vehicles and the resulting paints exposed to the weather. The lead silice-halides have excellent white color and fair hiding power and are'suitable for general application in oil. enamel andlacquer type paints and for other purposes where opaque white pigments are used. such as for rubber, 'linoleum and other a floor coverings, printing inks, vitrified enamel et cetera.

Intheoperation ofmyprocessIcanuseeither litharge (PbO) or other compounds of lead which upon heating supply to the product only PbO, such, for example, as red lead (PbsOs), lead peroxide (PhOs) and white lead (ZPbCOsPbHsOr) monium halide salts, which by reaction during the process supply to the product only the halogen, and volatilise other components of the halogen compound used.

lilrstthoroughlymixandmilltnematerials in the required proportions thereby reducing partlcle sise and assuring a close association of ingredients. -A porcelain or silex mill lining is satisfactory to avoid contamination of materials.

In case a solid accelerator, such as an .ammoniumhalidesait,isused,thechargemaybe dry-milled but preferably I nrst-wet-mill the'silice and lead compounds together and then add the halogsncompound as a solution and continue milling until the halogen is completely fixed as shown by absence of any halogen in;the solution. If the halogen compound is a solution of an ammonium salt, ammonia is liberated. The slurry discharged from the mill may be partially dewatered and dried if desired.

Either the wet pulp or the dry mixture-is then charged into the heating furnace. A furnace lining of high-grade fire brick is satisfactory to avoid contamination of materials. Means should be provided for control of temperature. In fur- .and complete before the charge has reached a temperature at which lead oxide and silica combine.

Lead oxide and silica alone react very slowly at a temperature of 500 C. but at 550 C. a. white lead silicate can be made by heating for a period of about 48 hours. While such temperatures are obviously impractical for making lead silicates from mixtures of lead compounds and sflica only, even lower temperature can be used if an accelerating and stabilizing compound of the class be-- fore referred to is used. My lead silico-halide pigments can be made in the temperature range 350 to 650 C. Preferred temperature ranges for the different types of lead silico-halides with variations in amount and kind of halide compound will be shown later by examples.

The time required in the calcinizing zone of the furnace depends upon the temperature and composition of the charge: the higher the temperature within the permissible range the shorter the time. The time required to complete the reaction may vary from minutes to several hours but it is usually desirable to hold the charge at the proper.temperature a little longer than appears absolutely, necessary to insure that the reaction is complete. The progress of the reaction during calcination may be judged by withdrawing a sampie from the furnace for inspection. The finished product should be substantially white and should not acquire a yellower ordarker color upon milling or grinding the sample in a mortar.

Lead silico-halide pigments, if not calcined at too high a temperature, are soft in texture and fine enough to be used as pigments for paint,but if desired the calcined pigment may be milled. Either dry or wet-milling methods may be used.

The following examples show' the working of my process and indicate the nature and composition of a few of the many possible lead silicohalide pigments. The products in all cases were found to be stable white pigments when tested by exposure to sunlight. 1

Example 1.Lead since chloride 7 To a mixture of 55 parts of lead oxide (P130) and 45 parts of silica enough water was added to form a thick slurry and the mixture milledfor 1% hours. 10 parts of ammonium chloride in 100 parts of water were then added-*to the mill charge, the milling continued for 54; hour longer. and the mixture dewatered and dried. The dry material was then calcined for 6 hours in the temperature range 420 to 450 C. The composition of the resulting white pigment was:

Lead oxide (PbO) 33.58% Silica 42.67% h smcate Lead chloride 23.75%

The pigment had a tinting strength of 140 compared with that of standard basic carbonate white lead taken as 100.

Example 2.-Lead silico-chloride A mixture of 79.6 parts of lead oxide (PbO), 10.6 parts of silica and 19.5 parts of ammonium chloride was made into a thick slurry with water, milled for hour and then dewatered and dried. The mixture was then calcined for 3 hours in the temperature range 460 to 480 C. The composition of the resulting white pigment was:

Lead oxide (PbO) 39.40% Silica 10.60% }Normal lead silicate Lead chloride 50.00%

The pigment had a tinting strength of 140 compared with that of standard basic carbonate white lead taken as 100.

Example 3.Lead silico-chlon'de A mixture of 79.8 parts of lead oxide (PhD) and 5.35 parts of silica was made into a thick slurry with water and milled for /2 hour. 53.72 parts of commercial hydrochloric acid, equivalent to 19.33 parts of actual HCl, diluted with 100 parts of water was then added and the milling continued for $4; hour longer. The mixture was dewatered and dried and then calcined for hour in the temperature range 530 to 550 C. The composition of the resulting white pigment was:

Leadoxide (PbO) 19.65%

silica }Normal lead silicate Lead chloride 75.00%

The pigment had a tinting strength of compared with that of standard basic carbonate white lead taken as 100.

Example 4.Lead silica-fluoride A mixture of 81.7 parts of lead oxide (PbO), 16.05 parts of silica and 7.55 parts of ammonium fluoride was made into a thick slurry with water, milled for hour and then dewatered and dried. The mixture was then calcined for 1 hour in the temperature range 500 to 530 C. The composition of the resulting white pigment was:

Lead oxide (Pb0) 58.95% silica }Normal lead silicate Lead fluoride 25.00%

The pigment had a tinting strength'of 7500mpared with that of standard basic carbonate white lead taken as 100.

Example 5.Lead silica-fluoride A mixture of 84.7 parts of lead oxide (PbO), 10.7 parts of silica and 15.1 parts of ammonium fluoride was made into a thick slurry with water;

' milled for /2 hour and then dewatered and dried.

The mixture was then calcined for V4 hour in the temperature range 390 to 410C. The composition of the resulting white pigment was:

Le xid P I gg i iii gi figggfilqormal leadsilicate Lead fluoride 50.00%

The pigment hada tinting strength of 65 compared with that of standard basic carbonate white lead taken as 100.

Example lit-Lead since-bromide A mixture of 74.2 parts of lead oxide (PbO), 16 parts of silica and 18.3 parts of ammonium bromide was made into a thick slurry with water; milled V2 hour and then dewatered and dried. The mixture was then calcined for 2 hours in the temperature range 550 to 570 C. The composition oi the resulting white pigment was:

Lead oxide (PbO)- 59.00% Sm 16.00% }Normal lead silicate Lead bromide 25.00%

The pigment had a tinting strength of 110 compared with that or standard basic carbonate white lead taken as 100.

Example 7 .Lead silica-bromide A mixture of 69.7 parts of lead oxide (PbO), 10.6 parts of silica and 26.7 parts of ammonium bromide was made into a thick slurry with water; milled for /2 hour and then dewatered and dried. The mixture was then calcined for V hour at 380 to 400 C. The composition of the resulting white pigment was:

Lead oxide (Pb) 39.35% silica }Normal lead silicate Lead bromide 50.00%

The pigment had a tinting strength of 210 compared with that of standard basic carbonate white lead taken as 100.

I claim as my invention:

7 1. An opaque white pigment consisting of lead oxide, silica and lead halide in chemical combination, the halide being selected from the group consisting of the chloride, fluoride and bromide of lead and the halogen being in amount more than of the total weight of lead calculated as PhD and silica.

2. An opaque white pigment consisting of lead oxide, silica and lead chloride in chemical com.- bination, the chlorine being in amount more than 5% of the total weight of lead calculated as PbO and silica.

3. An opaque white pigment consisting of lead oxide, silica and lead fluoride in chemical combination, the fluorine being in amount more than 5% of the total weight of lead calculated as PhD and silica.

4. An opaque white pigment consisting oi lead oxide, silica and lead bromide in chemical combination, the bromine being in amount more than 5% 01' the total weight of lead calculated as PhD and silica.

5. The method of making an opaque, white, lead silico-halide pigment which consists in intimately mixing lead and silicon compounds and a halogen compound selected from the group consisting of chlorides, fluorides and bromides, which upon heating will supply respectively only lead oxide (Pbo), silica and a halogen, the halogen being in amount more than 5% of the total weight of lead calculated as PbO and silica, and the halogen compound used consisting of halogen combined with a component which is volatilized at the temperature of reaction, and then heating the mixture at a temperature sufliciently high to chemically combine the ingredients in the solid phase without iusion to form said pigment.

6. The method of making an opaque, white, lead silico-halide pigment which consists in intimately mixing'lead oxide (Pb0), silica and a halogen compound selected from the group conupon heating will supply only the halogen, the halogen being in'amount more than 5%.o1the total weight oi lead calculated asPbO and silica, and the halog mpound used consisting oi halogen combined with a component which is volatilized at the temperature or reaction, and then heating the mixture in the temperature range 350 to 850 C. to chemically combine the ingredients in the solid phase without fusion to form said pigment.

7. The method 0! making an opaque. white,

lead silico-chloride pigment which consists in intimately mixing lead and silicon compounds and a chlorine compound which upon heating will supply respectively only lead oxide (PbO), silica and chloride, the chlorine being in amount more than 5% of the total weight of lead calculated as PbO and silica, and the chlorin compound used consisting of chlorine combined with a component which is volatilized at the temperature of reaction, and then heating the mixture at a temperature sufliciently high to chemically combine the ingredients in the solid phase without fusion to form said pigment.

8. The method of making an opaque, white, lead silico-chloride pigment which consists in intimately mixing'lead oxide (PbO), silica and a chlorine compound which upon heating will supply only chlorine, the chlorine being in amount more than 5% of the total weight of lead calculated as PhD and silica, and the chlorine compound used consisting oi chlorine combined with a component which is volatilized at the temperature of reaction, and then heating the mixture in 5 the temperature range. 350 to 550 C. to chemically combine the ingredients in the solid phase without fusion to form said pigment.

9. The method of making an opaque, white, lead silico-fluoride pigment which consists in inso timately mixing lead and silicon compounds and and silica, and the fluorine compound used consisting of fluorine combined with a component which is volatilized at the temperature of reaction, and then heating the mixture at a temperature sufllciently high to chemically combine the ingredients in the solid phase without fusion to form said pigment.

10. The method oi. making an op que, white, lead silica-fluoride pigment which consists in intimately mixing lead oxide (PbO), silica and a fluorine compound which upon heating will supply only fluorine, the fluorine being in amount more than 5% oi. the total weight of lead calculated as PhD and silica, and the fluorine compound used consisting of fluorine combined with a component which is volatilized at the temperature of reaction, and then heating the mixture in the temperature range 350 to 550 C. to chemically combine the ingredients in the solid phase without fusion to form said pigment.

11. The method oi making an opaque, white,

lead silica-bromide pigment which consists in intimately mixing lead and silicon compounds and a bromine compound which 1 9" heating will supplyrespectively only lead oxide (PbO), silica sisting of clfloridea fluoride! 8nd bromides. which 15 reacticn.-and then heating the mixture at-a temperature sufllciently high to chemically combine lated aa' PbO and silica, and the bromine compound used consisting oi bromine combined witha component which is volatilized at the temperature oi reaction, and then heating the mixture in the temperature range 350 to 550 C. to chemically combine the ingredient: in the solid phase without fusion to form said pigment.

oms n. mp0s. 

